Pack Lethality: Weaver, right, is the matriarch of Animal Kingdoms gangster family.s gangster family.

Survival of the fittest is the prevailing theme of Animal Kingdom, the assured feature debut of Australian writer-director David Michôd. So you don’t expect much from its barely-there, mouth-breathing protagonist, Joshua “J” Cody (James Frecheville), who’s first introduced staring at a game show on the telly and sitting next to a passed-out woman. Except replace “passed-out” with “dead” and “woman” with “mom.” J casually tells the EMTs who eventually arrive that it’s likely a heroin overdose, then calls his estranged grandmother, explaining in a monotone that he needs her help arranging a funeral and whatnot, because the 17-year-old admittedly doesn’t really know what to do.

Grandma’s reaction is the second indication that the Cody family ain’t quite right. Upon hearing news of her daughter’s death, Janine (Jacki Weaver) coos her sympathies and is all smiles when she comes to pick up J and move him into her home. It’s then we find out she’s a den mother to a brotherhood of criminals, all uncles to J from whom his mother shielded him. In a voiceover, J muses that she did so “because she was scared. I think they were all scared, even if they didn’t show it.” They don’t show it; instead, they shoot off their mouths and their guns, sometimes enlisting J’s help for more innocuous adventures such as threatening some douchebag on the road “to show him who’s king.”

The alpha dog in this circle is eldest son Pope (an oily Ben Mendelsohn), who spends the opening of the film in hiding, wanted by both the cops and other gangsters. When he does show up at Janine’s, he immediately takes over, enlisting J’s help in a plot to seek revenge for a family colleague who is murdered after being spotted with Pope. Two policemen die. Now J is no longer “invisible” (as he once observes when a bathroom hand dryer fails to start for him) and can’t hang with his girlfriend, Nicky (Laura Wheelwright), without endangering her life, too.

For all its drugs and criminality, Animal Kingdom is decidedly low-key. There’s rarely any bluster preceding its violence; Michôd instead opts for quiet and sometimes eerie tension, as in a scene in which a seemingly abandoned car, in the middle of a road with its doors swung open, serves as bait for the cops the Codys kill. Pope constantly asks others for their confidence (particularly one of his brothers, whom he suspects is gay), and though it’s ostensibly out of concern, you know he’s really trying to sniff out weakness. It’s a detective (Guy Pearce) who spells out to J the film’s titular metaphor, explaining that in the Australian bush it’s a constant battle of strong versus weak. Naturally, he suggests J would be among the strong for ratting out his family. J’s not so sure.

Frecheville gives an aptly infuriating performance as the mostly passive nephew, but it’s Mendelsohn and Weaver whom you’ll remember. The latter’s squat, well-appointed Janine is especially intriguing, kissing her kids on the mouth, cooking for them, and baring her teeth in grins instead of growls even when she starts playing as dirty as her cubs. Developments in the final chapter are also unforgettable—but they wouldn’t be nearly as shocking without Michôd’s accomplished control of the story’s steady boil.